In the field of overload protection devices it is well known that overload relays are provided for protecting components connected to an electrical circuit in the event the current flowing through the circuit exceeds a predetermined level. An overload relay monitors the current flowing in the protected circuit and sends a signal to cause a contactor in the protected circuit to open when the current flowing in the protected circuit is higher than a preselected level. Conventionally, this is accomplished by an electromechanical trip mechanism which opens a normally closed contact, thereby opening the contactor and removing power to the protected circuit. In a "self-powered" overload relay, the overload relay is powered by one or more current transformers which monitor the protected circuit. The current transformer(s) also provide power to the electromechanical trip mechanism. Therefore, only a small amount of power is available to the overload relay trip mechanism. In conventional overload relay devices, a solenoid is used to convert electrical energy to mechanical energy in order to open the contacts. Because a limited amount of power is supplied to the overload relay device, it is desirable to minimize the mechanical forces required to operate the mechanism employed for opening the contacts.
When an overload condition is experienced, power is supplied to a solenoid in the electromechanical trip mechanism causing a plunger to retract, which subsequently, through a series of levers or other mechanical components, causes the normally closed contacts to open. After the contacts have been opened, it is well known to manually return the opening or unlatching mechanism to its original position. However, residual magnetism in the solenoid may cause the plunger to remain in the retracted position. This increases the required force to be overcome by the return spring.
It is well known that overload relay devices are available with auxiliary contacts. Auxiliary contacts are used for alarms or other warning systems to alert one that the protected circuit has been interrupted. Such auxiliary contacts may be configured to be normally open or normally closed. Auxiliary contacts typically require a biasing spring external to the mechanism, thus requiring the return spring of the mechanism to overcome an additional load when tripped. Further, the applicants are not aware of any prior art devices which provide for selectively alternating between the normally open or normally closed positions without replacing one auxiliary switch with another auxiliary switch.